The present invention relates to a fuel intake control system for a supercharged internal combustion engine.
The Japanese Laid-open Patent Publication No. 55-137314, laid open to public inspection on Oct. 27, 1980, discloses a fuel intake system for a supercharged engine which comprises a primary intake system and an auxiliary intake system including a supercharger driven by a drive unit, for example, the engine. This prior art fuel intake system is so designed that, when and so long as the load on the engine is smaller than a predetermined value, only the primary intake system is brought into operation to supply a combustible air-fuel mixture into the engine through an associated primary intake port, but when and so long as the load on the engine is larger than the predetermined value and at least during the period in which the engine undergoes the compression stroke, the auxiliary intake system is brought into operation together with the primary intake system to allow a supercharged air from the supercharger to be supplied into the engine through an associated auxiliary intake port.
This prior art system appears advantageous in that, since the supercharger is driven by the engine in contrast to a turbocharger driven by exhaust gases emitted from the engine, the supply of the supercharged air into the engine would not be short of the required amount even at a low speed engine operating condition during which the flow of the exhaust gases through the exhaust manifold tends to be retarded.
This publication also discloses the use of an auxiliary throttle valve, situated in the auxiliary intake passage downstream of the supercharger with respect to the direction of flow of the supercharged air towards the engine, and also a relief passage having a relief valve and bypassing the supercharger. The auxiliary throttle valve employed therein is so positioned and so designed as to allow the supply of the supercharged air in correspondence with change in load imposed on the engine.
However, in view of the fact that the supercharger is driven by the engine with its discharge pressure variable according to the engine speed and irrespective of the magnitude of the load on the engine, the supercharged pressure, that is, the pressure of the supercharged air emerging from the supercharger, tends to be high during a certain engine operating condition in which, while the supercharger is operated, the opening of the auxiliary throttle valve is small. This tendency is enhanced particularly during a low load and high speed engine operating condition in which, while the supercharger is driven at a high speed, the opening of the auxiliary throttle valve is small. This results in the increased driving resistance (torque) to the supercharger with the consequent increase of the fuel consumption of the engine. The increased driving resistance brings about the overheating of the supercharger which will adversely affect the servicing life of the supercharger. In addition, the increase of the driving resistance to the supercharger which takes place at the initial stage of the driving of the supercharger is likely to result in the abrupt change in engine power output.